The present invention relates to novel (R)-2-octanol dehydrogenases useful for producing alcohols, ketones, particularly for producing optically active alcohols such as (S)-4-halo-3-hydroxybutyric acid esters and (R)-propoxybenzene derivatives, DNAs encoding the enzyme, methods for producing the enzymes, and methods for producing alcohols, ketones, particularly for producing optically active alcohols such as (S)-4-halo-3-hydroxybutyric acid esters and (R)-propoxybenzene derivatives using the enzymes.
(S)-4-halo-3-hydroxybutyric acid esters are compounds used as intermediates in synthesizing HMG-CoA reductase inhibitors, D-camitine, etc. These compounds are useful for syntheses of medicines and pesticides. Especially, how to get (to synthesize or separate) optically pure enantiomers of (S)-4-halo-3-hydroxybutyric acid esters is industrially important problem. So far, asymmetric synthesis, crystallization, and asymmetric reduction method using microorganisms such as baker""s yeast (Unexamined Published Japanese Patent Application (JP-A) Sho 61-146191, JP-A Hei 6-209782, and such) are known as methods for producing (S)-4-halo-3-hydroxybutyric acid esters. However, these known methods are inappropriate for industrial use because of the problems such as low optical purities of products, low yield, etc.
In addition, enzymes that reduce 4-haloacetoacetic acid esters to (S)-4-halo-3-hydroxybutyric acid estersare also being searched. For example, enzymes indicated below are known. The methods for synthesizing (S)4-halo-3-hydroxybutyric acid esters using these enzymes are reported. These enzymes are, however, reductases that use reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) as a coenzyme. Therefore, synthesizing (S)-4-halo-3-hydroxybutyric acid esters using these enzymes requires addition and regeneration of NADPH, which is expensive and chemically unstable, and is industrially disadvantageous.
Some reductases derived from baker""s yeast (D-enzyme-1, D-enzyme-2, J. Am. Chem. Soc., 107:2993-2994, 1985)
Aldehyde reductase 2 derived from Sporobolomyces salmonicolor (Appl. Environ. Microbiol., 65:5207-5211, 1999)
Keto pantothenic acid ester reductase derived from Candida macedoniensis (Arch. Biochem. Biophys., 294:469-474, 1992)
4-Chloroacetoacetic acid ethyl ester reductase derived from Geotrichum candidum (Enzyme Microb. Technol. 14, 731-738, 1992)
Carbonyl reductase derived from Candida magnoliae (WO 98/35025)
Carbonyl reductase derived from Kluyveromyces lactis (JP-A Hei 11-187869)
xcex2-Ketoacyl-acyl carrier protein reductase as one of fatty acid synthases type II (JP-A 2000-189170)
Although 3xcex1-hydroxysteroid dehydrogenase (JP-A Hei 1-277494), glycerol dehydrogenase (Tetrahedron Lett. 29, 2453-2454, 1988), and alcohol dehydrogenase derived from Pseudomonas sp. PED (J. Org. Chem., 57:1526-1532, 1992) are known as reductases using reduced form of nicotinamide adenine dinucleotide (NADH) as a electron donor, these enzymes are industrially disadvantageous because the activity of reaction for synthesizing (S)-4-halo-3-hydroxybutyric acid esters is low.
As indicated above, known methods for producing (S)-4-halo-3-hydroxybutyric acid esters using microorganisms and enzymes were not satisfactory in some respects such as optical purities, yields, activities, etc. These problems have made known methods difficult for industrial use.
On the other hand, (R)-propoxybenzene derivatives (JP-A Hei 02-732) are useful compounds as intermediates in synthesizing medicines, especially, optically active substances of ofloxacin ((S)-(xe2x88x92)-9-fluoro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzooxazine-6-carboxylic acid, JP-A Sho 62-252790), which is synthetic antibacterial drugs. How to get (to synthesize or separate) optically pure enantiomers of these compounds is industrially important problem.
Asymmetric acylation of racemates of propoxybenzene derivatives using lipase and esterase (JP-A Hei 03-183489) is known as a method for producing (R)-propoxybenzene derivatives. In this method, a process to separate remaining raw materials and acylated products after acylation of (R) form and a process to deacylate the acylated products are required. Therefore, this known method is inappropriate for industrial use because these processes are complicated.
The method for asymmetric reduction of acetonyloxybenzene derivatives using microorganisms has been also reported. However, this known method is inappropriate for industrial use because optical purities of (R)-propoxybenzene derivatives produced is as low as 84 to 98% (JP-A Hei 03-183489) or 8.8 to 88.4% (JP-A Hei 05-68577) and because the concentration of substrate is also as low as 0.1 to 0.5%. As the method in which high optical purities can be obtained by asymmetric reduction, the method using carbonyl reductase produced by Candida magnoliae (JP-A 2000-175693) was reported to synthesize (R)-propoxybenzene derivatives whose optical purities are 99% or more. However, this carbonyl reductase uses NADPH as a coenzyme. Therefore, synthesizing (R)-propoxybenzene derivatives using this enzyme requires addition and regeneration of NADPH, which is expensive and chemically unstable, and is industrially disadvantageous.
An objective of the present invention is to provide novel enzymes that can reduce 4-haloacetoacetic acid esters using NADH as a coenzyme and produce (S)-4-halo-3-hydroxybutyric acid esters having high optical purities. Furthermore, an objective of the present invention is to provide methods for producing, using the enzyme, (S)-4-halo-3-hydroxybutyric acid esters having high optical purities.
In addition, an objective of the present invention is to provide novel enzymes that can produce optically highly pure (R)-propoxybenzene derivatives, which are useful as intermediates in synthesizing antibacterial drugs, using NADH as a coenzyme. Furthermore, an objective of the present invention is to provide methods for producing, using the enzyme, (R)-propoxybenzene derivatives that have high optical purities.
The present inventors thought that alcohol dehydrogenase that can use NADH as an electron donor was useful for industrial use. NADH is cheaper and chemically more stable than NADPH. To discover enzymes that can effectively produce optically active (S)-4-halo-3-hydroxybutyric acid esters, the present inventors screened for alcohol dehydrogenase which has high activity on (R)-2-octanol, which has the same configuration as that of (S)-4-halo-3-hydroxybutyric acid esters and which has long chain as long as that of 4-haloacetoacetic acid esters.
Previous findings reported the enzymes derived from Comamonas terrigena, Pichia sp. NRRL-Y-11328, and pseudomonas sp. SPD6 as secondary alcohol dehydrogenases that can oxidize (R)-2-octanol stereoselectively and have activities to produce 2-octanone. However, no report has been made that these enzymes can reduce 4-haloacetoacetic acid esters and produce (S)-4-halo-3-hydroxybutyne acid esters. Activities to produce (S)-4-halo-3-hydroxybutyric acid esters by reducing 4-haloacetoacetic acid esters whose carbonyl group is bound to bulky side chains are expected to be low because activities of these enzymes for (R)-2-octanol are not significantly higher than activities for secondary alcohol like 2-propanol, which has short side chains.
Therefore, the present inventors screened widely for microorganisms that possess enzymes having ability to oxidize (R)-2-octanol preferentially. As a result, they have discovered that the microorganisms belonging to the genera below possess enzymes having ability to oxidize (R)-2-octanol preferentially:
Genus Pichia
Genus Candida
Genus Ogataea
Specifically, microorganisms below are found to possess enzymes having ability to oxidize (R)-2-octanol preferentially.
Pichia finlandica 
Pichia jadinii 
Candida utilis 
Ogataea wickerhamii 
Moreover, the present inventors cultivated these microorganisms and purified enzymes that can oxidize (R)-2-octanol from the microorganisms. As a result of examination of properties of these enzymes, the enzymes were found to oxidize (R)-2-octanol highly stereoselectively and, furthermore, to oxidize many secondary alcohols other than (R)-2-octanol stereoselectively. The enzymes were also found not only to possess high activities to reduce 4-chloroacetoacetic acid ethyl ester and to produce (S)-4-chloro-3-hydroxybutyric acid esters but also to possess high activities to reduce 2-acetonyloxy-3,4-difluoronitrobenzene and produce 2,3-difluoro-6-nitro[[(R)-2-hydroxypropyl]oxy]benzene. Thus, the inventions were completed.
Specifically, the present invention relates to novel (R)-2-octanol dehydrogenase useful for producing alcohols, ketones, particularly for producing optically active alcohols such as (S)-4-halo-3-hydroxybutyric acid esters, DNA encoding the enzyme, methods for producing the enzyme, and methods for producing alcohols, ketones, particularly for producing optically active alcohols such as (S)-4-halo-3-hydroxybutyric acid esters and (R)-propoxybenzene derivatives using the enzyme.
[1] An (R)-2-octanol dehydrogenase having the following physicochemical properties (1) and (2):
(1) Action
i) The enzyme produces ketone by oxidizing alcohol using oxidized form of xcex2-nicotinamide adenine dinucleotide as a coenzyme, and
ii) The enzyme produces alcohol by reducing ketone using reduced form of xcex2-nicotinamide adenine dinucleotide as a coenzyme, and
(2) Substrate specificity
i) The enzyme preferentially oxidizes (R)-2-octanol of two optical isomers of 2-octanol, and
ii) The enzyme produces (S)-4-halo-3-hydroxybutyric acid esters by reducing 4-haloacetoacetic acid esters.
[2] The (R)-2-octanol dehydrogenase of [1] having the following physicochemical properties (3) and (4):
(3) Optimum pH
Optimum pH for the oxidation reaction ranges from 8.0 to 11.0, and that for the reduction ranges from 5.0 to 6.5, and
(4) Substrate specificity
i) The enzyme shows higher activity on secondary alcohols than on primary alcohols, and
ii) The enzyme shows significantly higher activity on (R)-2-octanol than on 2-propanol.
[3] The (R)-2-octanol dehydrogenase of [1] or [2], wherein the (R)-2-octanol dehydrogenase is derived from a microorganism selected from the group consisting of the genus Pichia, genus Candida, and genus Ogataea.
[4] The (R)-2-octanol dehydrogenase of [3], wherein the microorganism belonging to the genus Pichia is Pichia finlandica. 
[5] The (R)-2-octanol dehydrogenase of [3], wherein the microorganism belonging to the genus Pichia is Pichia jadinii. 
[6] The (R)-2-octanol dehydrogenase of [3], wherein the microorganism belonging to the genus Candida is Candida utilis. 
[7] The (R)-2-octanol dehydrogenase of [3], wherein the microorganism belonging to the genus Ogataea is Ogataea wickerhamii. 
[8] A method for producing the (R)-2-octanol dehydrogenase of [1] or [2], the method comprising cultivating a microorganism selected from the group consisting of the genus Pichia, genus Candida, and the genus Ogataea, the microorganism producing the enzyme of [1] or [2].
[9] An isolated polynucleotide of (a) to (e) below, the polynucleotide encoding a protein having activity of (R)-2-octanol dehydrogenase:
(a) a polynucleotide comprising the nucleotide sequence of SEQ ID NO:1,
(b) a polynucleotide encoding a protein comprising the amino acid sequence of SEQ ID NO:2,
(c) a polynucleotide encoding a protein comprising the amino acid sequence of SEQ ID NO:2 in which one or more amino acids are replaced, deleted, inserted, and/or added,
(d) a polynucleotide hybridizing under stringent conditions with a polynucleotide comprising the nucleotide sequence of SEQ ID NO:1, and
(e) a polynucleotide encoding an amino acid sequence having not less than 70% homology to the amino acid sequence of SEQ ID NO:2.
As used herein, an xe2x80x9cisolated polynucleotidexe2x80x9d is a polynucleotide, the structure of which is not identical to that of any naturally occurring nucleic acid or to that of any fragment of a naturally occurring genomic nucleic acid spanning more than three genes. The term therefore covers, for example, (a) a DNA which has the sequence of part of a naturally occurring genomic DNA molecule but is not flanked by both of the coding sequences that flank that part of the molecule in the genome of the organism in which it naturally occurs; (b) a nucleic acid incorporated into a vector or into the genomic DNA of a prokaryote or eukaryote in a manner such that the resulting molecule is not identical to any naturally occurring vector or genomic DNA; (c) a separate molecule such as a cDNA, a genomic fragment, a fragment produced by polymerase chain reaction (PCR), or a restriction fragment; and (d) a recombinant nucleotide sequence that is part of a hybrid gene, i.e., a gene encoding a fusion protein. Specifically excluded from this definition are nucleic acids present in random, uncharacterized mixtures of different DNA molecules, transfected cells, or cell clones, e.g., as these occur in a DNA library such as a cDNA or genomic DNA library.
Accordingly, in one aspect, the invention provides an isolated polynucleotide that encodes a polypeptide described herein or a fragment thereof. Preferably, the isolated polynucleotide includes a nucleotide sequence that is at least 60% identical to the nucleotide sequence shown in SEQ ID NO:1. More preferably, the isolated nucleic acid molecule is at least 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or more, identical to the nucleotide sequence shown in SEQ ID NO:1. In the case of an isolated polynucleotide which is longer than or equivalent in length to the reference sequence, e.g., SEQ ID NO:1, the comparison is made with the fill length of the reference sequence. Where the isolated polynucleotide is shorter that the reference sequence, e.g., shorter than SEQ ID NO:1, the comparison is made to a segment of the reference sequence of the same length (excluding any loop required by the homology calculation).
[10] A substantially pure protein encoded by the polynucleotide of [9].
The term xe2x80x9csubstantially purexe2x80x9d as used herein in reference to a given protein or polypeptide means that the protein or polypeptide is substantially free from other biological macromolecules. For example, the substantially pure protein or polypeptide is at least 75%, 80, 85, 95, or 99% pure by dry weight. Purity can be measured by any appropriate standard method known in the art, for example, by column chromatography, polyacrylamide gel electrophoresis, or HPLC analysis.
[11] A recombinant vector into which the polynucleotide of [9] is inserted.
[12] The recombinant vector of [11], wherein a polynucleotide encoding a dehydrogenase that can catalyze oxidation-reduction reaction using xcex2-nicotiramide adenine dinucleotide as a coenzyme is further inserted.
[13] A transformant comprising the polynucleotide of [9] or the vector of [11] in an expressible manner.
[14] A method for producing the protein of [10], the method comprising cultivating the transformant of [13].
[15] A method for producing a alcohol, the method comprising reacting the (R)-2-octanol dehydrogenase of [1] or [2], the protein of [10], a microorganism producing the enzyme or the protein, or a processed product of the microorganism with a ketone to reduce the ketone.
[16] The method of [15], wherein the microorganism is the transformant of [13].
[17] The method of [15], wherein the ketone is a 4-haloacetoacetic acid ester derivative and wherein the alcohol is an (S)-4-halo-3-hydroxybutyric acid ester derivative.
[18] The method of [17], wherein the 4-haloacetoacetic acid ester derivative is 4-chloroacetoacetic acid ethyl ester and wherein the alcohol is (S)-4-chloro-3-hydroxybutyric acid ethyl ester.
[19] The method of [15], wherein the ketone is an acetonyloxybenzene derivative represented by the generic formula 1:
Generic Formula 1
where each of x1 and x2 indicates a halogen atom, and wherein the alcohol is a propoxybenzene derivative represented by the generic formula 2:
Generic Formula 2 
[20] The method of [19], wherein the acetonyloxybenzene derivative is 2-acetonyloxy-3,4-difluoronitrobenzene and wherein the alcohol is 2,3-difluoro-6-nitro[[(R)-2-hydroxypropyl]oxy]benzene.
[21] The method of [15], the method further additionally comprising converting oxidized form of xcex2-nicotinamide adenine dinucleotide into reduced form thereof.
[22] A method for producing a ketone, the method comprising reacting the (R)-2-octanol dehydrogenase of [1] or [2], the protein of [10], a microorganism producing the enzyme or the protein, or a processed product of the microorganism with an alcohol to oxidize the alcohol.
[23] A method for producing an optically active alcohol, the method comprising the steps of reacting the (R)-2-octanol dehydrogenase of [1] or [2], the protein of [10], a microorganism producing the enzymes or the protein, or a processed product of the microorganism with a racemic alcohol to preferentially oxidize either optical isomer, and obtaining the remaining optically active alcohol.
[24] The method of [22] or [23], the method further additionally comprising converting reduced form of xcex2-nicotinamnide adenine dinucleotide into oxidized form thereof.
The present invention provides enzymes having the following physicochemical properties (1) and (2):
(1) Action
i) The enzyme produces ketone by oxidizing alcohol using oxidized form of xcex2-nicotinamide adenine dinucleotide (NAD+) as a coenzyme, and
ii) The enzyme produces alcohol by reducing ketone using reduced form of xcex2-nicotinamide adenine dinucleotide (NADH) as a coenzyme, and
(2) Substrate specificity
i) The enzyme preferentially oxidizes (R)-2-octanol of two optical isomers of 2-octanol, and
ii) The enzyme produces (S)-4-halo-3-hydroxybutyric acid esters by reducing 4-haloacetoacetic acid esters.
Preferably, the enzymes of the present invention further have the following enzymatic properties (3) and (4):
(3) Optimum pH
Optimum pH for the oxidation reaction ranges from 8.0 to 11.0, and that for the reduction ranges from 5.0 to 6.5, and
(4) Substrate specificity
i) The enzyme shows higher activity on secondary alcohols than on primary alcohols, and
ii) The enzyme shows significantly higher activity on (R)-2-octanol than on 2-propanol.
Furthermore, preferable (R)-2-octanol dehydrogenases in this invention have the following physicochemical and enzymatic properties (5) to (8):
(5) Optimum working temperature range
The optimum temperature for the oxidation reaction of (R)-2-octanol ranges from 45xc2x0 C. to 55xc2x0 C. The optimum temperature for the reduction reaction of ethyl 4-chloroacetoacetate ranges from 55xc2x0 C. to 60xc2x0 C.
(6) Stable pH range
The enzyme is stable in the range of pH 8 to 9.
(7) Inhibition
The enzyme is slightly inhibited by mercury chloride and chelating agent ethylenediaminetetraacetic acid disodium salt (EDTA.2Na).
(8) Stabilization
The enzyme is stabilized by N-ethylmaleimide, o-phenanthroline, magnesium chloride, calcium chloride, and manganese chloride.
(9) Purification method
The enzyme of the present invention can be purified by usual purification methods from microorganisms producing the enzyme. For example, the enzyme can be purified by carrying out protamine sulfate precipitation after disrupting fungal bodies, by salting-out the centrifugal supernatant with ammonium sulfate, and further by combining anion-exchange chromatography, hydrophobic chromatography, affinity chromatography, gel filtration, etc.
The term xe2x80x9cdehydrogenasexe2x80x9d used herein means an enzyme that catalyzes dehydrogenation, that is, oxidation reaction in which hydrogens are removed from a compound including hydrogens. Furthermore, the enzyme possesses reduction activity on ketone and can catalyze reverse reaction of oxidation reaction under reductive conditions. Therefore, xe2x80x9cdehydrogenasexe2x80x9d in this invention possesses activity catalyzing reduction reaction that is reverse reaction of the oxidation reaction and in which hydrogens are added. In general, when possessing the same activities, enzymes called xe2x80x9cdehydrogenasexe2x80x9d, xe2x80x9coxidation-reduction enzymexe2x80x9d, xe2x80x9coxidasexe2x80x9d, xe2x80x9creductasexe2x80x9d, or the like are included in the xe2x80x9cdehydrogenasexe2x80x9d of this invention.
In the present invention, reduction activity on 4-chloroacetoacetic acid ester can be measured as follows. The activity can be validated by incubating at 30xc2x0 C. the reaction mixture containing potassium phosphate buffer (pH 6.5, 100 mM), 0.2 mM NADH, 20 mM ethyl 4-chloroacetoacetate, and the enzyme and by measuring decrease of absorbance at 340 nm accompanying decrease of NADH. 1 U was defined as the amount of the enzyme catalyzing decrease of 1 xcexcmol of NADH for 1 minute. Quantification of proteins can be done by dye binding method using the protein assay kit (BIORAD).
On the other hand, oxidation activity on (R)-2-octanol can be measured as follows. The activity can be validated by incubating at 30xc2x0 C. the reaction mixture containing Tris-HCl buffer (pH 8.5, 50 mM), 2.5 mM NAD+, 5 mM (R)-2-octanol, and the enzyme and by measuring increase of absorbance at 340 nm accompanying generation of NADH. 1 U was defined as the amount of the enzyme catalyzing generation of 1 xcexcmol of NADH for 1 minute.
(R)-2-octanol dehydrogenase of this invention has high oxidation activity on (R)-2-octanol. In addition, the oxidation activity on (R)-2-octanol of the enzyme is significantly higher than that on 2-propanol. Herein, when the rate of change in absorbance at 340 nm accompanying increase or decrease of NADH per unit time in contacting with (R)-2-octanol as a substance in the presence of NAD+ is twice or more and preferably five times or more larger as relative activity when taking the rate for 2-propanol as 1, it can be said that the dehydrogenase activity is significantly higher.
In this invention, that (R)-2-octanol dehydrogenase xe2x80x9cpreferentiallyxe2x80x9d oxidizes (R)-2-octanol means that the enzymatic activity of (R)-2-octanol dehydrogenase on S form is 50 or less, preferably 20 or less, and more preferably 10 or less when taking the activity on R form as 100.
(R)-2-octanol dehydrogenases having physicochemical properties as mentioned above can be obtained from culture of microorganisms producing this enzyme. For example, strains producing the enzyme of this invention can be found in the yeast of the genus Pichia, the genus Candida, and the genus Ogataea. Especially, Pichia finlandica and Pichia jadinii as the genus Pichia, Candida utilis as the genus Candida, and Ogataea wickerhamii as the genus Ogataea are excellent in ability to produce (R)-2-octanol dehydrogenase of this invention. Examples of strains available for obtaining the (R)-2-octanol dehydrogenase of this invention are as follows:
(i) Pichia finlandica: DSM 70280, DSM 1380
(ii) Pichia jadinii: DSM 2361, DSM 70167, IFO 0987
(iii) Candida utilis: IFO 0988, IFO 0626
(iv) Ogataea wickerhamii: IFO 1706
As for secondary alcohol dehydrogenase produced by Pichia finlandica, there is a report that showed 2-propanol dehydrogenase activity using cell-free extract (Biochimica et Biophysica Acta, 716:298-307, 1982). However, according to the additional test by the inventors, multiple 2-propanol dehydrogenases were included in the cell-free extract of this strain. On the other hand, the (R)-2-octanol dehydrogenase of this invention is a minor component having very weak 2-propanol dehydrogenase activity. Therefore, the (R)-2-octanol dehydrogenase of this invention is distinctly different from the enzymes describe in this reference.
The microorganisms mentioned above are cultivated in a general medium used for cultivation of fungi such as YM medium. The desired enzymes can be well obtained especially from Pichia finlandica using either of glucose, glycerol, or methanol as carbon source in the medium. The desired enzymes can be well obtained from Candida utilis using, in particular, methanol as carbon source in the culture medium. Fungus bodies are recovered after enough proliferation and disrupted in a buffer to which reducing agents like 2-mercaptoethanol and such and protease inhibitors like phenylmethansulfonyl fluoride PMFS are added to make cell-free extract. The enzyme can be purified from cell-free extract by combining fractionation of proteins based on their solubility, various chromatographies, etc. As methods for fractionation of proteins based on their solubility, for example, precipitation with organic solvent such as acetone or dimethylsulfoxide, salting out with ammonium sulfate, or the like can be used. On the other hand, as chromatographies, cation exchange chromatography, anion exchange chromatography, gel filtration, hydrophobic chromatography, and many affinity chromatographies using chelates, pigments, antibodies, and such are known. More specifically, through hydrophobic chromatography with Phenyl-Toyopearl, anion exchange chromatography with DEAE-Sepharose, hydrophobic chromatography with Butyl-Toyopearl, affinity chromatography with Blue-Sepharose, gel filtration with Superdex 200, and such, the enzyme can be purified to electrophoretically almost single band.
The present invention relates to polynucleotides encoding (R)-2-octanol dehydrogenases and their homologues. In this invention, polynucleotides can be naturally existing polynucleotides such as DNAs or RNAs and can be also polynucleotides including artificially synthesized nucleotide derivatives.
The polynucleotide encoding the (R)-2-octanol dehydrogenase of the present invention comprises, for example, the nucleotide sequence of SEQ ID NO:1. The nucleotide sequence of SEQ ID NO:1 encodes a polypeptide comprising the amino acid sequence of SEQ ID NO:2. The polypeptide comprising this amino acid sequence constitutes preferred embodiments of the (R)-2-octanol dehydrogenase of the present invention.
The polynucleotide of the present invention includes a polynucleotide encoding a polypeptide having above-mentioned physicochemical properties (1) and (2) as well as comprising the amino acid sequence of SEQ ID NO:2 in which one or more amino acids are deleted, substituted, inserted, and/or added. One skilled in the art can properly introduce substitution, deletion, insertion, and/or addition mutation into the DNA comprising the nucleotide sequence of SEQ ID NO:1 by site-specific mutagenesis (Nucleic Acid Res., 10:6487, 1982: Methods in Enzymol., 100:448, 1983; Molecular Cloning 2nd Ed., Cold Spring Harbor Laboratory Press (1989), PCR: A Practical Approach, IRL Press, pp. 200 (1991)).
The number of amino acids that are mutated is not particularly restricted, as long as the (R)-2-octanol dehydrogenase activity is maintained. Normally, it is within 50 amino acids, preferably within 30 amino acids, more preferably within 10 amino acids, and even more preferably within 3 amino acids. The site of mutation may be any site, as long as the (R)-2-octanol dehydrogenase activity is maintained. An amino acid substitution is preferably mutated into different amino acid(s) in which the properties of the amino acid side-chain are conserved. A xe2x80x9cconservative amino acid substitutionxe2x80x9d is a replacement of one amino acid residue belonging to one of the following groups having a chemically similar side chain with another amino acid in the same group. Groups of amino acid residues having similar side chains have been defined in the art. These groups include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, aspargine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine).
In addition, the polynucleotide of the present invention includes polynucleotides hybridizing under stringent conditions to the DNA comprising the nucleotide sequence of SEQ ID NO:1 as well as encoding a protein having above-mentioned physicochemical properties (1) and (2). The xe2x80x9cpolynucleotide hybridizing under stringent conditionsxe2x80x9d means a polynucleotide hybridizing to a probe nucleotide that has one or more segments of at least 20 consecutive nucleotides, preferably at least 30 consecutive nucleotides, for example, 40, 60, or 100 consecutive nucleotides, arbitrarily selected from the sequence in the nucleotide sequence shown in SEQ ID NO:1, by using, for example, ECL Direct Nucleic Acid Labeling and Detection System (Amersham-Pharmacia Biotech) under conditions recommended in the attached manual (washing with the primary wash buffer containing 0.5xc3x97SSC at 42xc2x0 C.).
Also included in the invention is a polynucleotide that hybridizes under high stringency conditions to the nucleotide sequence of SEQ ID NO:1 or a segment thereof as described herein. xe2x80x9cHigh stringency conditionsxe2x80x9d refers to hybridization in 6xc3x97SSC at about 45xc2x0 C., followed by one or more washes in 0.2xc3x97SSC, 0.1% SDS at 65xc2x0 C.
Polynucleotides that can hybridize with DNA comprising the nucleotide sequence of SEQ ID NO:1 under stringent conditions include those comprising nucleotide sequences similar to SEQ ID NO:1. It is highly possible that such polynucleotides encode proteins functionally equivalent to the protein comprising the amino acid sequence of SEQ ID NO:2.
Furthermore, the polynucleotide of the present invention includes a polynucleotide encoding a protein exhibiting percent identity of at least 70%, preferably at least 80% or 90%, more preferably 95% or more to the amino acid sequence of SEQ ID NO:2. As used herein, xe2x80x9cpercent identityxe2x80x9d of two amino acid sequences, or of two nucleic acid sequences, is determined using the algorithm of Karlin and Altschul (PNAS USA, 87:2264-2268, 1990), modified as in Karlin and Altschul, PNAS USA, 90:5873-5877, 1993). Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al. (J. Mol. Biol., 215:403-410, 1990). BLAST nucleotide searches are performed with the NBLAST program, score=100, wordlength=12. BLAST protein searches are performed with the XBLAST program, score=50, wordlength=3. To obtain gapped alignment for comparison purposes GappedBLAST is utilized as described in Altschul et al. (Nucleic Acids Res., 25:3389-3402, 1997). When utilizing BLAST and GappedBLAST programs the default parameters of the respective programs (e.g., XBLAST and NBLAST) are used to obtain nucleotide sequences homologous to a nucleic acid molecule of the invention. Homology search of protein can readily be performed, for example, on the Internet, for example, in databases related to amino acid sequences of protein, such as SWISS-PROT, PIR, and such; databases related to DNAs, such as DNA Databank of JAPAN (DDBJ), EMBL, GenBank, and such; databases related to deduced amino acid sequences based on DNA sequences; and such by using the FASTA program, BLAST program, etc. As a result of homology search in SWISS-PROT using BLAST program and amino acid sequence of SEQ ID NO:2, the protein that showed the highest homology among known proteins was glucose dehydrogenase of Bacillus subtilis which showed 43% identity and 61% Positives. Not less than 70% homology in this invention indicates, for example, the value of homology in Positive using BLAST program.
In this invention, a polynucleotide encoding a protein having the physicochemical properties (1) and (2) above is especially called xe2x80x9chomologuexe2x80x9d to a polynucleotide comprising the nucleotide sequence of SEQ ID NO:1 . Homologues can be isolated by PCR cloning and hybridization from other organisms based on the nucleotide sequence of SEQ ID NO:1, in addition to by mutation introduction. For example, the nucleotide sequence of SEQ ID NO:1 is that of the gene isolated from Pichia finlandica. Besides, a polynucleotide encoding a protein that has the physicochemical properties (1) and (2) above and that can be obtained from a microorganism such as Pichia jadinii, Candida utilis as a yeast belonging to the genus Candida, Ogataea wickerhamii as a yeast belonging to the genus Ogataea, and so on is included in this invention.
The polynucleotides of this invention are useful for genetic engineering production of the (R)-2-octanol dehydrogenase of this invention. Alternatively, microorganisms having (R)-2-octanol dehydrogenase activity that is useful for producing ketones and alcohols can be produced by genetic engineering using the polynucleotides of this invention
The present invention encompasses an (R)-2-octanol dehydrogenase having the amino acid sequence of SEQ ID NO:2 and having above-mentioned physicochemical properties (1) and (2) as well as homologues thereof. The protein comprising the amino acid sequence of SEQ ID NO:2 constitutes preferred embodiments of the (R)-2-octanol dehydrogenase of the present invention.
The homologue of the (R)-2-octanol dehydrogenase of the present invention comprises the amino acid sequence of SEQ ID NO:2 in which one or more amino acids are deleted, substituted, inserted, and/or added. One skilled in the art can readily obtain a DNA encoding such a homologue of the (R)-2-octanol dehydrogenase by properly introducing substitution, deletion, insertion, and/or addition mutation into the DNA comprising the nucleotide sequence of SEQ ID NO:1 by site-specific mutagenesis (Nucleic Acid Res., 10:6487, 1982; Methods in Enzymol., 100:448, 1983; Molecular Cloning 2nd Ed., Cold Spring Harbor Laboratory Press (1989), PCR: A Practical Approach IRL Press pp. 200 (1991)) or the like. The homologue of the (R)-2-octanol dehydrogenase of SEQ ID NO:2 is available by introducing into a host a DNA encoding the homologue of the (R)-2-octanol dehydrogenase and expressing it in the host.
Furthermore, the homologue of the (R)-2-octanol dehydrogenase of the present invention includes a protein exhibiting percent identity of at least 70%, preferably at least 80% or 90%, more preferably 95% or more to the amino acid sequence of SEQ ID NO:2. Homology search of protein can readily be performed, for example, on the Internet, for example, in databases related to amino acid sequences of protein, such as SWISS-PROT, PIR, and such; databases related to DNAs, such as DNA Databank of JAPAN (SWISS-PROT), EMBL, GenBank, and such; databases related to deduced amino acid sequences based on DNA sequences; and such by using the FASTA program, BLAST program, etc. As a result of homology search in SWISS-PROT using BLAST program and amino acid sequence of SEQ ID NO:2, the protein that showed the highest homology among known proteins was glucose dehydrogenase of Bacillus subtilis which showed 43% identity and 61% Positives. Not less than 70% homology in this invention indicates, for example, the value of homology in Positive using BLAST program.
The DNA encoding the (R)-2-octanol dehydrogenase of the present invention may be isolated, for example, by using the following procedure.
After purification of the enzyme of this invention, multiple amino acid sequences can be determined by analyzing N-terminal amino acid sequences, and further, by cleaving the protein using enzymes such as lysyl endopeptidase, V8 protease, and such, by purifying peptide fragments by reverse-phase liquid chromatography and such, and by analyzing amino acid sequence with protein sequencer.
If partial amino acid sequences are revealed, nucleotide sequences encoding the amino acid sequences can be inferred. The DNA fragment of this invention can be obtained by PCR by designing primers for PCR based on the inferred nucleotide sequences or the nucleotide sequence of SEQ ID NO:1 and by using chromosomal DNA or cDNA library of the enzyme-producing strain as a template.
Furthermore, using the obtained DNA fragment as a probe, the DNA of this invention can be obtained by colony or plaque hybridization using a library obtained by transforming E. coli with a phage or plasmid into which restriction enzyme digestion products of the chromosomal DNA of the enzyme-producing strain are introduced or a cDNA library.
In addition, the DNA of the present invention can be obtained by analyzing the nucleotide sequence of the DNA fragment obtained by PCR, by designing PCR primers, based on the sequence already obtained, to extend the DNA outward, by digesting, with an appropriate restriction enzyme(s), the chromosomal DNA of the strain producing the enzyme of interest and then, by performing inverse PCR (Genetics, 120:621-623, 1988) using the self-ligated circular DNA as a template; or alternatively by using RACE method (Rapid Amplification of cDNA End; xe2x80x9cExperimental manual for PCRxe2x80x9d pp. 25-33, HBJ Press).
The DNA of the present invention includes not only the genomic DNA and cDNA cloned by the above-mentioned methods but also chemically synthesized DNA.
The thus-isolated DNA encoding the (R)-2-octanol dehydrogenase of the present invention is inserted into a known expression vector to provide a (R)-2-octanol dehydrogenase-expressing vector. Further, by culturing cells transformed with the expression vector, the (R)-2-octanol dehydrogenase of the present invention can be obtained from the transformed cells.
In the present invention, there is no restriction on the microorganism to be transformed for expressing (R)-2-octanol dehydrogenase whose coenzyme is NAD+, as long as the organism is capable of being transformed with the vector containing the DNA encoding the polypeptide with activity of (R)-2-octanol dehydrogenase whose coenzyme is NAD+ and capable of expressing activity of (R)-2-octanol dehydrogenase whose coenzyme is NAD+. Available microorganisms are those for which host-vector systems are available and include, for example:
bacteria such as the genus Escherichia, the genus Bacillus, the genus Pseudomonas, the genus Serratia, the genus Brevibacterium, the genus Corynebacterium, the genus Streptococcus, and the genus Lactobacillus;
actinomycetes such as the genus Rhodococcus and the genus Streptomyces;
yeasts such as the genus Saccharomyces, the genus Kluyveromyces, the genus Schizosaccharomyces, the genus Zygosaccharomyces, the genus Yarrowia, the genus Trichosporon, the genus Rhodosporidium, the genus Pichia, and the genus Candida; and
fungi such as the genus Neurospora, the genus Aspergillus, the genus Cephalosporium, and the genus Trichoderma; etc.
Procedure for preparation of a transformant and construction of a recombinant vector suitable for a host can be carried out by employing techniques that are commonly used in the fields of molecular biology, bioengineering, and genetic engineering (for example, see Sambrook et al., xe2x80x9cMolecular Cloningxe2x80x9d, Cold Spring Harbor Laboratories). In order to express, in a microorganism, the gene encoding the (R)-2-octanol dehydrogenase of the present invention whose coenzyme is NAD+, it is necessary to introduce the DNA into a plasmid vector or phage vector that is stable in the microorganism and to let the genetic information transcribed and translated. To do so, a promoter, a unit for regulating transcription and translation, is placed upstream of the 5xe2x80x2 end of the DNA of the present invention, and preferably a terminator is placed downstream of the 3xe2x80x2 end of the DNA. The promoter and the terminator should be functional in the microorganism to be utilized as a host. Available vectors, promoters, and terminators for the above-mentioned various microorganisms are described in detail in xe2x80x9cFundamental Course in Microbiology (8): Genetic Engineeringxe2x80x9d, Kyoritsu Shuppan, specifically for yeasts, in xe2x80x9cAdv. Biochem. Eng. 43, 75-102(1990)xe2x80x9d and xe2x80x9cYeast 8, 423-488 (1992).xe2x80x9d
For example, for the genus Escherichia, in particular, for Escherichia coli, available plasmids include pBR series and pUC series plasmids; available promoters include promoters derived from lac (derived from xcex2-galactosidase gene), trp (derived from the tryptophan operon), tac and trc (which are chimeras of lac and trp), PL and PR of xcex phage, etc. Available terminators are derived from trpA, phages, rrnB ribosomal RNA, etc.
For the genus Bacillus, available vectors are pUB110 series and pC194 series plasmids; the vectors can be integrated into host chromosome. Available promoters and terminators are derived from apr (alkaline protease), npr (neutral protease), amy (xcex1-amylase), etc.
For the genus Pseudomonas, there are host-vector systems developed for Pseudomonas putida and Pseudomonas cepacia. A broad-host-range vector, pKT240, (containing RSF1010-derived genes required for autonomous replication) based on TOL plasmid, which is involved in decomposition of toluene compounds, is available; a promoter and a terminator derived from the lipase gene (JP-A No. Hei 5-284973) are available.
For the genus Brevibacterium, in particular, for Brevibacterium lactofermentum, available plasmid vectors include pAJ43 (Gene, 39:281, 1985). Promoters and terminators used for Escherichia coli can be utilized without any modification for Brevibacterium.
For the genus Corynebacterium, in particular, for Corynebacterium glutamicum, plasmid vectors such as pCS11 (JP-A Sho 57-183799) and pCB101 (Mol. Gen. Genet., 196:175, 1984) are available.
For the genus Streptococcus, plasmid vectors such as pHV1301 (FEMS Microbiol. Lett., 26:239, 1985) and pGK1 (Appl. Environ. Microbiol., 50:94, 1985) can be used.
For the genus Lactobacillus, plasmid vectors such as pAMb1 (J. Bacteriol., 137:614, 1979), which was developed for the genus Streptococcus, can be utilized; and promoters that are used for Escherichia coli are also usable.
For the genus Rhodococcus, plasmid vectors isolated from Rhodococcus rhodochrous are available (J. Gen. Microbiol., 138:1003, 1992).
For the genus Streptomyces, plasmids can be constructed in accordance with the method as described in xe2x80x9cGenetic Manipulation of Streptomyces: A Laboratory Manualxe2x80x9d (Cold Spring Harbor Laboratories (1985)) by Hopwood et al. In particular, for Streptomyces lividans, pIJ486 (Mol. Gen. Genet., 203:468-478, 1986), pKC1064 (Gene, 103:97-99, 1991), and pUWL-KS (Gene, 165:149-150, 1995) are usable. The same plasmids can also be utilized for Streptomyces virginiae (Actinomycetol., 11:46-53, 1997).
For the genus Saccharomyces, in particular, for Saccharomyces cerevisiae, YRp series, YEp series, YCp series, and YIp series plasmids are available; integration vectors (refer EP 537456, etc.), which are integrated into chromosome via homologous recombination with multicopy-ribosomal genes, allow to introduce a gene of interest in multicopy and the gene incorporated is stably maintained in the microorganism; and thus, these types of vectors are highly useful. Available promoters and terminators are derived from genes encoding ADH (alcohol dehydrogenase), GAPDH (glyceraldehyde-3-phosphate dehydrogenase), PHO (acid phosphatase), GAL (xcex2-galactosidase), PGK (phosphoglycerate kinase), ENO (enolase), etc.
For the genus Kluyveromyces, in particular, for Kluyveromyces lactis, available plasmids are those such as 2-xcexcm plasmids derived from Saccharomyces cerevisiae, pKD1 series plasmids (J. Bacteriol., 145:382-390, 1981), plasmids derived from pGK11 and involved in the killer activity, KARS (Kluyveromyces autonomous replication sequence) plasmids, and plasmids (refer EP 537456, etc.) capable of being integrated into chromosome via homologous recombination with the ribosomal DNA. Promoters and terminators derived from ADH, PGK, and the like are available.
For the genus Schizosaccharomyces, it is possible to use plasmid vectors comprising ARS (autonomous replication sequence) derived from Schizosaccharomyces pombe and auxotrophy-complementing selectable markers derived from Saccharomyces cerevisiae (Mol. Cell. Biol., 6:80, 1986). Promoters such as ADH promoter derived from Schizosaccharomyces pombe are usable (EMBO J., 6:729, 1987). In particular, pAUR224 is commercially available from TaKaRa Shuzo Co., Ltd.
For the genus Zygosaccharomyces, plasmids originating from those such as pSB3 (Nucleic Acids Res., 13:4267, 1985) derived from Zygosaccharomyces rouxii are available; it is possible to use promoters such as PHO5 promoter derived from Saccharomyces cerevisiae and GAP-Zr (Glyceraldehyde-3-phosphate dehydrogenase) promoter (Agri. Biol. Chem., 54:2521, 1990) derived from Zygosaccharomyces rouxii. 
For the genus Pichia, host-vector systems originating from autonomous replication sequences (PARS1, PARS2) derived from Pichia have been developed (Mol. Cell. Biol., 5:3376, 1985), and it is possible to employ a highly efficient promoter such as methanol-inducible AOX promoter, which is available for high-cell-density-culture (Nucleic Acids Res., 15:3859, 1987). Host vector system is developed for Pichia angusta (previously called Hansenula polymorpha). Although autonomous replication sequences (HARS1 and HARS2) derived from Pichia angusta are available as vectors, they are rather unstable. Therefore, multicopy integration to chromosome is effective for them (Yeast, 7:431-443, 1991). In addition, promotors of AOX (alcohol oxidase) and FDH (formate dehydrogenase) induced by methanol and such are available.
For the genus Candida, host-vector systems have been developed for Candida maltosa, Candida ulbicans, Candida tropicalis, Cindida utilis, etc. An autonomous replication sequence originating from Candida maltosa has been cloned (Agri. Biol. Chem., 51:1587, 1987), and a vector using the sequence has been developed for Candida maltosa. Further, a chromosome-integration vector with a highly efficient promoter unit has been developed for Candida utilis (JP-A Hei 08-173170).
For the genus Aspergillus, Aspergillus niger and Aspergillus oryzae have intensively been studied among fungi, and thus plasmid vectors and chromosome-integration vectors are available, as well as promoters derived from an extracellular protease gene and amylase gene (Trends in Biotechnology, 7:283-287, 1989).
For the genus Trichoderma, host-vector systems have been developed for Trichoderma reesei, and promoters such as that derived from an extracellular cellulase gene are available (Biotechnology, 7:596-603, 1989).
There are various host-vector systems developed for plants and animals other than microorganisms; in particular, the systems include those of insect such as silkworm (Nature, 315:592-594, 1985), and plants such as rapeseed, maize, potato, etc. These systems are preferably employed to express a large amount of foreign protein.
Microorganisms that possess ability to produce 4-haloacetoacetic acid ester-reducing enzymes used in this invention include all strains, mutants, variants, and transformants that have ability to produce NAD+-dependent (R)-2-octanol dehydrogenase and that belong to the genus Pichia, the genus Candida, and the genus Ogataea, the transformants being constructed by genetic engineering and obtaining ability to produce the enzyme of this invention.
In addition, strains that express the (R)-2-octanol dehydrogenase of this invention obtained by the methods above are available for producing the enzymes of this invention and for producing secondary alcohols and ketones described below.
Thus, the present invention relates to the above-mentioned method for producing secondary alcohols by reducing ketones using (R)-2-octanol dehydrogenase. The (R)-2-octanol dehydrogenase of this invention can use NADH, which is cheaper and more stable than NADPH, as a coenzyme and, therefore, is advantageous for industrial use. The desired oxidation reaction can be carried out by contacting the enzyme of this invention, culture including the enzyme, or processed product thereof with reaction solution.
The forms of contacting the enzyme with reaction solution are not limited to these examples. In the reaction solution, substrate and NADH, which is a coenzyme necessary for the enzymatic reaction, are dissolved in suitable solvent giving environment desired for the expression of the enzymatic activity. Processed products of microorganisms including the (R)-2-octanol dehydrogenase of this invention specifically include microorganisms whose permeability of cell membrane is changed by treatment of organic solvent such as detergent, toluene, and such; cell-free extract obtained by disrupting fungus body with glass beads or by enzyme treatment; partially purified extract thereof; etc.
As ketones in the methods of this invention for producing secondary alcohols, acetophenon, 2-octanone, 4-haloacetoacetic acid ester derivatives, acetonyloxybenzene derivatives represented by the generic formula 1:
Generic Formula 1 
(where each of x1 and x2 indicates a halogen atom), bromomethylcyclopropylketone, 2-acetylbutyrolactone, 5-chrolo-2-pentanone are suitably used. 4-Haloacetoacetic acid ester derivatives in this invention are compounds obtained by replacing position 4 of acetoacetic acid ester with an arbitrary halogen atom. Alcohols constituting the above-mentioned acetoacetic acid ester can be any alcohols. Halogens of 4-haloacetoacetic acid ester derivatives can be bromine, chlorine, and iodine, and, in particular, chlorine is suitably used. Esters can be esters of alcohols that includes straight-chain, branched-chain, and aromatic substitution, such as methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, octyl ester, benzyl ester, and such, and ethyl ester is most preferably used. The 4-haloacetoacetic acid ester derivative includes a derivative including alkyl including straight chain or branched chain at position 2, or halogen such as chlorine, bromine, iodine, etc. Halogens of acetonyloxybenzene derivatives include bromine, chlorine, iodine, and fluorine, and, in particular, fluorine is preferably used. Especially, 2-acetonyloxy-3,4-difluoronitrobenzene is a useful compound that gives 2,3-difluoro-6-nitro-[[(R)-2-hydroxypropyl]oxy]benzene, which is an intermediate in synthesizing an antibacterial drug ofloxacin.
The present invention also relates to a method for producing ketones by oxidizing secondary alcohols with the above-mentioned (R)-2-octanol dehydrogenase. A ketone, which is a reaction product, can be produced by reacting the (R)-2-octanol dehydrogenase of this invention, microorganism producing the enzyme, or processed product thereof with a secondary alcohol. As secondary alcohols that can be substrates in this invention, alkyl alcohols having halogen or aromatic substitution, and so on, such as 2-propanol, 2-butanol, 2-octanol, 1-phenylethanol, and such can be used.
Furthermore, the enzyme of this invention, microorganism producing the enzyme, or processed product thereof can be used for producing optically active alcohols using asymmetric oxidation ability of (R)-2-octanol dehydrogenase with racemic alcohol as a substrate. In other words, optically active alcohol can be produced by preferentially oxidizing either optical isomer with the enzyme of this invention and by obtaining the remaining optically active alcohol. More specifically, the (R)-2-octanol dehydrogenase of this invention is reacted in the presence of NAD+ with racemates in which the (S) form and (R) form of 2-octanol or 1-phenylethanol are mixed. The (R)-2-octanol dehydrogenase of the present invention, which is excellent in stereoselectivity, acts specifically on the (R) form and oxidizes it to produce ketone. However, because it does not act on the (S) form of the alcohol, the proportion of the (S) form becomes larger gradually. If the (S) form accumulating in this way is separated, the (S) form of the alcohols can be finally recovered from racemates. In this way, (S)-2-octanol can be obtained from (RS)-2-ocatanol, and (S)-phenylethanol can be obtained from (RS)-phenylethanol.
The term xe2x80x9coptically active alcoholxe2x80x9d used herein means an alcohol that includes more optical isomer than other optical isomers, or an alcohol having enantiomeric excess (ee) of preferably 50% or more, more preferably 90% or more, and even more preferably 95% or more. Moreover, xe2x80x9coptical isomerxe2x80x9d of this invention can be generally called xe2x80x9coptically active substancexe2x80x9d or xe2x80x9cenantiomerxe2x80x9d.
The above-mentioned method for producing ketones according to this invention can be combined with regenerating system of NADH. NADH is generated from NAD+ concomitantly with the oxidation reaction catalyzed by (R)-2-octanol dehydrogenase. Regeneration of NAD+ from NADH can be effected by using an enzyme (system) contained in microorganisms, which enables regeneration of NAD+ from NADH or by adding to the reaction system a microorganism or an enzyme capable of producing NAD+ from NADH, for example, glutamate dehydrogenase, NADH oxidase, NADH dehydrogenase, and the like. Furthermore, utilizing the substrate specificity of the enzyme of the present invention, the substrate for the reduction reaction, such as 2-octanone, acetophenone, and such, may be added to the reaction system to concurrently effect regeneration of NAD+ from NADH by the action of the enzyme by itself.
In the same manner, the method for producing alcohols can be combined with regenerating system of NAD+. NAD+ is generated from NADH concomitantly with the reduction reaction. NAD+-reducing ability (e.g., glycolysis) of microorganisms can be utilized to regenerate NADH from NAD+. Such ability can be reinforced by adding glucose or ethanol to the reaction system. Alternatively, microorganisms capable of generating NADH from NAD+, or processed products or enzyme thereof may be added to the reaction system. Regeneration of NADH can be carried out using microorganisms containing formate dehydrogenase, glucose dehydrogenase, malate dehydrogenase, glycerol dehydrogenase, alcohol dehydrogenase, or the like, or processed products or purified enzyme thereof. For example, NADH can be regenerated using the conversion of glucose into xcex4-gluconolactone in the case of the glucose dehydrogenase above. Utilizing the property of the (R)-2-octanol dehydrogenase of the present invention, NADH can also be regenerated using the enzyme per se by adding the substrate for the oxidation reaction such as 2-octanol to the reaction system.
Reactants necessary for NADH regeneration reaction can be added to the reaction system for producing alcohol of the present invention as they are, or as their immobilized products. The reactants can also be contacted with the reaction system through a membrane that enables exchanging NADH.
When the microorganism transformed with a recombinant vector including the DNA of this invention is used alive for producing the above alcohol, an additional reaction system for NADH regeneration can be sometimes omitted. Namely, by using microorganisms that has high activity of NADH regeneration, efficient reduction reaction using transformants can be performed without adding enzymes for NADH regeneration. Moreover, by introducing, into a host, a gene for glucose dehydrogenase, formate dehydrogenase, alcohol dehydrogenase, amino acid dehydrogenase, organic acid dehydrogenase (for example, malate dehydrogenase, and such), and such, which are available for NADH regeneration, simultaneously with a DNA encoding the NAD+-dependent (R)-2-octanol dehydrogenase of the present invention, more efficient expression of the NADH regeneration enzyme and the NAD+-dependent (R)-2-octanol dehydrogenase, and reduction reaction can be performed. For introducing these two or more genes into a host, a method for transforming the host with multiple recombinant vectors obtained by separately introducing, to avoid incompatibility, the genes into multiple vectors whose replication origins are different, a method in which both genes are introduced into a single vector, or a method for introducing both genes into chromosomes is available.
Examples of glucose dehydrogenases that are available for NADH regeneration in this invention include a glucose dehydrogenase derived from Bacillus subtilis. In addition, Examples of formate dehydrogenases include a formate dehydrogenase derived from Mycobacterium vaccae. The genes encoding these enzymes have been already cloned. Alternatively, such genes can be obtained from the microorganisms by PCR or hybridization screening based on the revealed nucleotide sequences.
When multiple genes are introduced into single vector, each gene can be ligated to the region involved in the regulation of expression, such as promotor or terminater. Multiple genes can also be expressed as operon including multiple cistrons like lactose operon.
The oxidation reaction or reduction reaction using the enzyme of the present invention can be carried out in water, in a water-insoluble organic solvent such as ethyl acetate, butyl acetate, toluene, chloroform, n-hexane, etc., or in the two-phase system of such an organic solvent and aqueous medium such as ethanol, acetone, etc.
The reaction of the present invention can be achieved by using immobilized enzymes, embrane reactors, etc.
Enzymatic reaction by (R)-2-octanol dehydrogenase of this invention can be done under the following conditions:
reaction temperature: 4 to 60xc2x0 C., preferably 10 to 37xc2x0 C.
pH: 3 to 11, preferably 5 to 10, more preferably 6.0 to 9.0
concentration of substrate: 0.01 to 90%, preferably 0.1 to 30%
If necessary, 0.001 mM to 100 mM or preferably 0.01 to 10 mM coenzyme NAD+ or NADH can be added to the reaction system. Although the substrate can be added at once at the start of reaction, it is preferable to be added continually or discontinuously so as not to make the concentration of the substrate in the reaction mixture too high.
The compound to be added to the reaction system for regenerating NADH, include, for example, glucose in the case of using glucose dehydrogenase, formic acid in the case of using formate dehydrogenase, ethanol or 2-propanol in the case of the using alcohol dehydrogenase, and can be added at a molar ratio to a substrate ketone of 0.1:20, and preferably in 0.5 to 5 times excess amount to a substrate ketone. The enzymes for regenerating NADH such as glucose dehydrogenase, formate dehydrogenase, or alcohol dehydrogenase can be added in 0.1 to 100 times, and preferably 0.5 to 20 times amount of the enzymatic activity compared with that of the NAD+-dependent (R)-2-octanol dehydrogenase of the invention.
Alcohols produced by reduction of ketones and alcohols produced by asymmetric oxidation of racemic alcohols in this invention can be purified by properly combining centrifugation of microbial cells and proteins, separation by membrane treatment and such, solvent extraction, distillation, etc.
For example, as to 4-halo-3-hydroxybutyric acid esters, after a reaction mixture that includes microbial cells bodies is centrifuged to remove the microbial cells, a solvent such as ethyl acetate, toluene, and such is added to the supernatant to extract 4-halo-3-hydroxybutyric acid esters in the solvent layer. Distilling it after phase separation enables purifying highly pure 4-halo-3-hydroxybutyric acid esters.
The enzyme of this invention used for these various synthetic reactions is not limited to purified enzyme and includes partially purified enzyme, microbial cells including this enzyme, and processed product thereof. The term xe2x80x9cprocessed productxe2x80x9d used herein collectively means microbial cells, purified enzyme, partially purified enzyme, or the like that is fixed by various methods. The enzyme constituting the enzymatic reaction of this invention can be used in immobilized forms. The method for immobilization the enzyme is not particularly limited. For example, the methods for immobilizing the enzyme usin glutaraldehyde, acrylamide, xcexa-carrageenan, calcium alginate, ion exchange resin, Celite, and such are known. The reaction of this invention can be conducted using membrane reactor, etc. Membranes that can constitute a membrane reactor are exemplified by ultrafilter, hydrophobic membrane, cationic membrane, nanofiltration membrane (J. Ferment. Bioeng., 83:54-58, 1997) etc.
All references cited herein are incorporated by reference.